As for conventional aluminum alloys of good free-machinability there are known alloys such as AA 2011 and AA 6262. Alloy AA 2011 contains copper essentially and small amounts of a few elements of heavy metals. Alloy AA 6262 contains magnesium and silicon essentially and in addition, small amounts of a few elements of heavy metals. The former, however, is rather poor in corrosion resistance, while the latter, in spite of its considerably high corrosion resistance, has not always shown satisfactory performance in so far as its ability to be free cut is concerned.
Furthermore, various kinds of aluminum alloy products coated with paint are widely used. A typical manufacturing process of such products is as follows: After being worked to a final configuration from a bar or tubing of aluminum alloy, the product is subjected to anodic oxidation, followed by a coating process with acrylic resin paint and the paint is then baked or cured to provide weather-proof coating. During such curing operation, the product is generally heated to a rather high temperature of about 160.degree. C. and it has been widely recognized that the oxidized surface on products of such conventional aluminum alloys is apt to peel off from the substrate.
Accordingly, it has long been desired to provide an aluminum alloy which has excellent free-machinability and corrosion resistance and is further free from peeling off of anodically oxidized surfaces after being heat-treated at an elevated temperature enough to cure acrylic paint.